Magnetostrictive transducer



y 1952 H. .1. MQCREARY 3,033,944

MAGNETOSTRICTIVE TRANSDUCER Filed Dec. 51, 1957 INVENTOR. HAROLD J. M CREARY -tro-acoustic function.

United States Patent aware Filed Dec. 31, 1957, Ser. No. 706,438 3 Claims. (Cl. 179-110) This invention relates to electrical-to-mechanical transducers and more particularly to those using magnetostrictive action.

It is an object of the present invention to provide an improved transducer for use in receivers, loudspeakers, or other electro-acoustical devices.

Generally in the past magnetostrictive transducers have utilized bi-metallic members as the basic effect producer. Due ,to the rigidity of the bi-metallic member, its usefulness was in part limited.

The present invention provides for the use of a flexible material such as rubber or plastic having impregnated therein metal particles of ferrite materials which have a high coercive force. This material may then be used in loudspeakers or receivers to provide a medium which can be magnetostrictively influenced to perform the elec- A material of the type which may be used herein is shown in an article, A New Magnetostrictive Material by H. E. Strauss shown on p. 267 Journal of Kpplied Physics, February 1954. Other ferrite materials of almost any known type may be used within the elastic matrix to accomplish the desired result.

Shown are three transducer embodiments using this material. FIG. 1 shows a cone type permanent magnet loudspeaker.

FIG. 2 shows a second cone type loudspeaker.

FIG. 3 shows a receiver for use in such instances as telephone receivers or hearing aids.

FIG. 1 shows a loudspeaker having a cone 11 of paper or other suitable material. Supporting the cone is a support member or spider 12. At the vertex of the cone is the electro magnet which includes core 13 having winding coiled about it and magnetic iron discs 14 and 17. Both discs are firmly attached to the core 13. Core 13 is composed ofa cylinder constructed of a rubber compound such as neoprene which has embedded within it a heavy dispersion of ferritic particles. For maximum effectiveness the ferritic particles should be of a highly-oriented barium ferrite which has permanent magnet qualities. Other ferritic materials may be utilized, however their effectiveness would be of varying'degrees of value since a permanent magnetic effect would be advisable. This effect could be achieved in two other ways; first, providing a common permanent magnet in conjunction with the speaker or, second; introducing a steady direct current to the winding 15 and superimposing the pulsating current on the steady current. For the purpose of simplicity, it will be assumed herein that an oriented ferrite is embedded in the rubber matrix to provide this feature. The core 13 is surrounded by an outer structure which is primarily a hollow cylindrical tube 16 also fabricated from the rubbery material with ferrite particles embedded in it.

Thus, when a pulsating current such as that generated by voice frequency is impressed on coil 15, the core 13 is energized. A magnetic path is completed from core 13 through upper metal plate 14, tube 16 and through lower metal plate 17 to the core. The rubber materials will tend to expand and contract under the control of their internal magnetic particles. It is assumed that the lower plate 17 is restrained from movement by the speaker structure. Thus due to the expansions and contractions of the resilient members of the magnetic path,

i.e., core 13 and tube 16, the upper magnetic plate 14 is oscillated at the input frequency. The cone 11 by virtue of its connection to disc 14 is also oscillated toeffect an audio output from the loudspeaker.

FIG. 2 shows a structure, generally similar to FIG. 1. The embodiment of FIG. 2 comprises a toroidal core 24 made of any suitable magnetically responsive material which core has surrounding it a shell 23 composed of the rubbery matrix having the ferritic particles embedded in it. A spider 22 encloses the shell and has permanently secured within it the shell 23. The shell at its upper end is connected to the vertex of cone 21. The base edges of cone 21 are connected to spider 22 in a movable manner.

The operation of this embodiment is similar to the operation of FIG. 1. Coil 25 and core 24 on energiza tion complete a magnetic path around the shell 23. The center portion of the shell expands longitudinally under the influence of the increase in magnetic field strength and will move the vertex of the cone 21 upward. Subsequent energizations and deenergizations of the coil 24 will cause the vertex of cone 21 to be oscillated vertically to produce an audio output.

The embodiment of FIG. 3 is especially useful for applications such as a telephone receiver or hearing aid receiver. The construction consists of a coil 34 having a winding 35. Surrounding the coil 34 is a rubber or similar resilient material formed in the bulb shape shown to conform to the ear contours of a human being. The bulb 33 contains the permanent magnet ferrite particles therein as in the previous embodiments. The structure of the bulb could be manufactured in either of two ways. First, the unit could be molded as a single entire bulb around the toroidal coil 34 using destructible cores for the cavities. Second, the structure could be manufactured in two sections, the parting line 39 dividing the sections. Then by the use of a suitable adhesive or cement the structure could be assembled permanently. Formed within the bulb is a sound box cavity 37 adjacent the coil 34 and having acapillary air tube 36 extending outward from sound cavity 37. Supports 38 are used to maintain the cavity and tube spacing and may be any form of suitable pin or stud. This construction in general is somewhat similar to that of present day hearing aid receivers and the principle of operation is somewhat similar also.

The operation of this embodiment is as follows: an audio input in the form of a pulsating current is fed to the winding 35 of coil 34. The coil 34 will therefore be energized and deenergized accordingly. The bulk 33 will respond to these energizations and deenergizations accordingly to expand and contract longitudinally. These movements will cause sound to be generated in the sound cavity 37 and emitted through the .air tube 36 to the ear of the bearer.

It may be readily seen by one skilled in the art that by use of the embodiment of FIG. 3 in place of the magnetic circuit of FIG. 2, a multi-axial speaker having a wide range of frequency response may be encountered. Also it may be seen that the embodiments shown are but a few of the possible transducer uses possible in view of the present invention.

What is claimed is:

1. Means for moving a column of air to produce an audio output, said means comprising a sidewall encircling said column, said sidewall constructed of material magnetically actuatable by a changing magnetic field to expand and contract, means for producing a changing magnetic field internally within said sidewall to cause said sidewall to expand and contract thereby vibrating said air column to produce a sound output.

2. An electro-acoustic transducer having an electromagnetic coil, a closedmagnetic path encircling said coil, said path comprising a flexible non-magnetic material having embedded therein particles of a rigid, high permeability ferrite, said coil responsive to energizations and deenergizations to cause said entire magnetic path to oscillate, an enclosed cavity Within said path expanded and contracted in response to said oscillations, said cavity having a capillary acoustic tube coupled thereto for com binedly generating an audio output dependent on said oscillations.

Y 3. A hearing aid speaker comprising a toroidal wound coil, a bulb encircling said coil and forming a closed mag netic path for the field produced by said coil, said bulb shaped in conformity with the contours of a human ear, said bulb comprising a solid rubbery matrix having dispersed internally in said matrix magnetic flakes of high coercive force, a sound cavity and adjacent capillary tube disposed Within said bulb, said magnetic flakes controlled by energizations and deenergizations of said coil to expand and contract the matrix and cause sound to be formed in the cavity and transmitted outwardly from said cavity by means of said capillary tube.

References (Cited in the file of this patent UNITED STATES PATENTS 1,486,866 De Forest Mar. 18, 1924 1,961,149 Hoffman'et al. June 5, 1934 2,532,876 Asche et al. Dec. 5, 1950 2,550,771 Camp May 1, 1951 2,638,577 Harris May 12, 1953 2,648,837 Mounce Aug. 11, 1953 FOREIGN PATENTS Great Britain Apr. 15, 1935 

